Analysis of a ${\rm TE}_{22,6}$ 118-Ghz Quasi-Optical Mode Converter

A quasi-optical mode converter for the European TE22,6 118-GHz gyrotron has been continuously improved for long pulse operation. Measurements at the last generation show a double peak structure at the output window plane, but simulations have not been able to explain this behavior in the past.The overall output system was analyzed carefully. Besides measurements, the first full 3-D electromagnetic analysis of a complete quasi-optical mode converter was performed. This gives the indication of the double-peak structure at the output window plane. An enhancement of the system for a single-peak Gaussian-like output beam will be presented.